T I 



500 



T I S 



nd the cytob.at is perfectly clear and transparent, and 

 prubalily tilli-il with an aqueous fluid, luid i boiiiuli-il by 

 the surrounding mucous granules, pressed back by 

 puuion. Rut i il u-' mucous 



granule* may almost shaking the 



Uge of the' micros., long 



..il. a they cntirclv dissolve in a few minutes in dis- 

 tilled water, leaving the cytoblasts behind. The vesicle 

 gradually gets larger an.! - mure consistent, its 



}, mg formed entirely of vegetable gelatine (Gal- 

 . jit tlir cvtohlast. which alwavs forms a portion 

 of tin 1 wall. The whole cell now gradual! v enlarges ! 

 the edges of the cytoblast. ami gets so large, that at last 

 t!u- latter appears as a small body enclosed in one of the 

 side this jioiiit the cyt'oblast assumes the cha- 



racter of the nreula described by Hrown. 'Hie young eell 

 frequently presents great irregularities, a proof th;it the 

 expansion does not proceed regularly from a fixed jiiiint. 

 The cell groin progressively, and become*, under the in- 



flucnce of surrounding objects, more rcgvilar, and most 

 frequently assumes tin- form of a rhomboidal do i 

 The cytoolast still remains in the cell, partaking of the 

 life inherent in the cell, unless it is in cells destined to a 

 higher development, when it is either reabsorted in the 

 walls of the cell, or cast off into the cell as a useless mem- 

 ber, and there reabsorbed. It is only after the rcabsorp- 

 tionof the cytoblaM that seconda.'V K positions are observed 

 to commence on the inside of the ivalls of the cell. 

 (Schleiden.) 



The cytoblast remains in the cells in only a small num- 

 ber of cases. They are found in a portion ofthe cellular tissue 

 of Orchidacc;e. also of < 'aclai , :e. In hairs likewise, and 

 cells in which the function of c\ ; vied on, they arc 



very frequently permanent: also in the pollen granules ol 

 Abietin:e. Di. Schleiden always found them present in 

 recently-formed cellular tissue. 



The increase of the bulk and -i/.\- of plants depends upon 

 the development, in the interior of the old or oiigiimlh 

 formed cells, of several new cvtohlasts. each of which 

 develops a new cell, and causes b\ its presence tlu 

 absorption or destruction ofthe old one. 



But all the parts of plants do not cou-i-t of simple cells : 

 the cells become elongated, forming libioiis or woody tis- 

 sue, and spiral tilircs are generated both in cells and lubes, 

 i'uting tin- various forms of til.ro-ccllular and vascu- 

 lar tissue, and it will he i a lew words on 

 their development. One great error that lias arisen from 

 the naming and classification of the tissues of the plant: 

 has been the supposition that they were essentially distinc 

 and possessed a dill in. This is seen in the 

 theories of the origin of wood. Woody fibres are nothing 

 more than elongated cells with thickened walls; but the) 

 opposed to originate in a different manner from tin 

 cellular tissue; and an ingenious theory of Du Peti' 

 Thouars has been adopted by many eminent botanists foi 

 the purpose of explaining this phenomenon. 



In referring to Du Petit Thouars' views. Dr. Ijndleysays, 

 'The wood is not formed out of the bark as a mere deposi- 

 tion, but it is produced from matter elaborated in the leave. 

 downwards, cither through tin i the inne 



bark along with the matter for forming the liber, by vvhicl 

 it is subsequently parted with, or it and the liber are 

 nitlcd distinct from one another, the one adhering It 

 the albumen, the other to the bark. I know of no proo 

 ofthe former supposition; of the latter there is every rea 

 ton to believe the truth.' And again, 'It is not merely in 

 the property of increasing the species that bud- arrec v'vitl 

 seeds, but that they emit roots in like manner : and Ilia 

 the wood and liber are both formed by the dow- 



nt of bud-roots, at first nourished by the moi- 

 the cambium, and finally imbedded in the ccllula 

 which is the result of the organization of that set-ration. 

 This theory then supposes that woody tissue is sent dowi 

 as a deposit from buds and leaves. But it is much too 

 general, anil whatever may be the agency of the leaves ii 

 -ating the sap, and preparing the secretions of plants 

 they are certainly not the only agent* engaged in develop 

 ing the woody tissue. There are many parts of plan' 

 pOMe no leaves, and some whole orders, u Cactacea- 

 that potftcss no leaves that yet develop woody tissue 

 Trees alto that have the hark removed in a circle from tin 

 tern at the spring of the year, before the leaves are de 

 TelopeU, will at the end of the year exhibit between thi 



rk and wood new woody tissue. This was proved by a 

 of experiments performed on Dr. 



-inkester. Tin- existence of w t| 1( . 



ark of trees is also another fact oppos IVtit 



fliouars' theory. These ex i '-\i-t in the ('..-m of 



cnobs. and are most frequent on the beech, projecting from 

 lie bark of the tree. >n e\amining them it will be found 

 hat they have no connection with th 

 mil consist of several layers of contoii 



.1 in a bark ot'lheir own, consisting of liber aiu! 

 ular integument. They are of all si/cs. from a men' point 



i he smallest consist of cellular 1 



.n the centre of which a darker spot is seen, as though. the 

 lissue wns injured or diseased. It is around this spot that 

 ihe fibres of woody tissue develop themselves. These 

 liodies a])|X':ir to have their origin in an undeveloped bud : 

 lience they are called by Dnt rochet rniliri/n-l,inl\ ; but as 

 they goon increasing in size, and development occurs in 

 a circular, rather than a longitudinal direction, they are de- 

 scrihcd by I.inkester as abortirt- hrunrhes. From th. 

 searches of Schleiden there can be little doubt but that the 

 elongated tissue is developed in the same manner as i 



tion that still arises, and requires solution 

 whether the single lihrcs of woody tissue are the produce 

 of a single cvtoblast or of several. In t ailed 



pitted or lSothrcnch\ma. there are evident indications of 

 its cylindrical tubes being form- ,al cells i; 



together, and the walls, being absorbed at their point of 

 union, have thus produced a continuous tube. 



The above observations of Schleiden have set aside the 

 supposition that the cell d entirely of spiral 



fibres intimately siipci |Ki-cd. liut still the question recurs 

 a.s to whether tibre may not be generated independent of 

 membrane. Meycn found fibres without membrane in the 

 genus Sti-H* ; I,mdley obscived them in Cnllnmiti : and 

 many oilier instances are known in which fibres are found 

 in punt* without anv apparently enveloping membrane. 

 The late researches of Dr. Martin Harry on the develop- 

 ment of animal tissue from the spiial fibre of the hlood- 

 b'loliule have induced some botanists to examine this < 

 tion ; and Dr. 'U'illshirc, in a paper in the ilth volume of the 

 Annals of Natural ll\^, dcavourcd to prove 



that the irregular-shaped liodies marked with dark lines, 

 and found in the juices of many plants, arc tin 

 of pure lihrous tissue. If such a development of fibre ' 

 place, it can lie only in exceedingly i: Schleiden 



in his memoir on Phylogenesis stales that lihrcs arc never 

 formed free, but always in the interior of cells, and that the 

 walls of these cells in thcjmmg state are simple and of 

 a very delicate texture'. 



\Vhclher tibrc is formed independent of membrane or 

 not. there is no doubt of ils formation in a large number ol 

 - in the inside of cells and tubes forming the fibro- 

 11 and fibro-vascular tissues, A< Schk-idcn. 



the cells in which the development of iihre take-, place are 

 in the commencement of the formation of the fibres tilled 

 with starch, rarely with mucus or gum, although the starch 

 passes into the state of mucus or gum. and then into that of 

 gelatin i gallcrtc i. From this latter vegetable fibn - 

 formed which in their development always follow the direc- 

 tion of a spiral line, whose coils are narrower or widei 

 iiiigto circumstances. The development of the tilue 

 is the same in the spiral vessel as in the spiral cell, there 

 being no difference between the two but in their dimen- 

 In tlu> first volume of the 'Transactions of the 

 Microscopic. il Society of London" (1*1-.! . Mr. Quekctt 

 give- the following account of the development of fibre in 

 the vascular tissue of plants: 'When the voung \< 

 ;that is. membranous tulles'! are n co- ar as 



pellucid glossy tubes, with a rylohlast in some part of 

 their interior: earlier than this they arc not to lie icadiiy 

 recognised from cell*. As they grow older tin 

 diminishes, and the contents, which at fiisl and 



gelatinous, become le-, tiansparcnt Irani containing thou- 

 sands of granules, which are too small In allow of the pas- 

 sage of light, and consequent >'. nits: 

 these atoms are about (lie ,^,0!' an inch in diameter, and 

 have the motion known aa" act i vi .'' If the vessel 

 be wounded at this period contents pour 

 slowly out, and then the of these 

 molecules are still more cl' These atoms, from 

 their freedom of motion, are arranged nn! iy in 

 the interior of the vc^d, but in a short time, some of them 



